Describing a tension tester as an example of a test machine used for the universal material test, this tension tester 1 is shown in FIG. 1 and comprises a base 10, a gate-shaped support frame 11 disposed on an upper face of the base 10 and opened on its front and rear sides, upper and lower chucks 12 and 13 provided at upper and lower positions of the base 10, respectively to grapes the test piece 4 and a load mechanism 2 for tension load provided on one of the chucks, which is the upper chuck 12 in the illustrated example through a load cell 14, for example. The other chuck, which is the lower chuck 13 in the illustrated example, is securely attached to the base 10.
The load mechanism for tension load comprises a servo motor 21 disposed below the base 10, two ball screws 18 contained in the support frame 11 on both sides there and rotated by the servo motor 21 and a crosshead 17 meshed with the ball screws 18 and moved in upward and downward directions by rotation of the ball screws 18. The upper chuck 12 is suspended from and supported by the crosshead 17 through the load cell 14. Thus, as the crosshead 17 vertically moves in the upward and downward directions, tension load is applied to the test piece 4 and the actual tension load applied to the test piece 4 is detected by information from the load cell 14.
In a conventional material test method using such an apparatus, the tension load is applied to the test piece with predetermined speed (a crosshead speed of 0.1 mm/min., for example) until it reaches the load assumed to reach a break point of the test material (500 N through 300 KN, for example) and variation in strain while the tension load is being applied to the test material is subsequently measured to obtain a yield point and the break point of the test material, for example.
The technique of testing the material by applying the predetermined load to the test material at the suitably set up speed is a generally common one in the measurement test for specifying the mechanical properties of the material such as the tension test, the compression test and the bending test and continues from former times to present times.
The aforementioned conventional technique can obtain the general strain, the yield point, the break point and so on of the test piece, but its principal object is that the load such as tension, compression etc. is continuously applied to the test piece at the preset speed until the objective phenomena (the break, for example) appears and there has been not noticed variation in the true strain occurring in the test piece when certain load is applied thereto. In other words, for example, in the measurement of the yield point where plastic deformation of the material starts, there appears the phenomena that the strain is slowly advancing in long time under the fixed load and therefore in the conventional measurement depending on the tension speed, the measurement is made in the state where the strain is still advancing and in an unstable condition. Thus, the next load is applied to the test piece before the strain beginning to occur at certain load point stops, which causes the problem of the reliability of the measurement value and the basis thereof.
Therefore, there are some cases where the same material would have various strain speeds depending on the set tension speed (the speed corresponding to the movement speed of the crosshead, in the aforementioned example) and would have different strain speed depending on the applied load. In the conventional test method having such a viewpoint not aimed, there is a problem in which the true mechanical properties of the material have not been obtained.
Since the test apparatus for carrying out the aforementioned conventional test method has not been designed from such a viewpoint, an operator can work only paying attention to what speed at which the load should be applied to the test piece, how correctly the strain should be measured or how correctly the yield point and the break point should be measured. Even though the computer technology, which has accomplished a remarkable development in recent years, is used, the precision and the automation of the measurement have been just asked for without having gotten out of the conventional measurement viewpoint.
The object of the invention is to provide a universal material test method and a test apparatus suitable for carrying out this test method adapted to be able to judge the property or the treatment process of a material by measuring a time in which the strain of the material gets stable under a new viewpoint that strain of the material varies on change of the component of the material and change of organization of the material when it is treated and especially thermally treated when constant load is applied to the material, which fundamentally changes from the point view of the prior art material test method.